75.1 Functions and Variables for opsubst

The function opsubst is similar to the function subst, except that
opsubst only makes substitutions for the operators in an expression. In general,
When f is an operator in the expression e, substitute g
for f in the expression e.

To determine the operator, opsubst sets inflag to true. This means
opsubst substitutes for the internal, not the displayed, operator
in the expression.